1. Field of the Invention
The invention relates generally to prismatic structures configured to maximize light control and particularly to splitting prisms having conventionally non-linear surfaces capable of directing light incident thereon away from impingement on adjacent prisms and therefore out of a light-transmissive luminaire body or the like such that the directed light is available for illumination.
2. Description of the Prior Art
Prismatic structures, or prisms, have been known for centuries to be useful in a variety of applications including incorporation into light transmissive “globes” and the like for use in luminaires of varying description. U.S. Pat. No. 563,836 issued in 1896 to Blondel et al discloses “globes, shades, reflectors, and other envelops” useful in luminaires and having prisms molded or otherwise formed on such globes for the purpose of reflecting, refracting and directing light rays in a desired manner. For purposes of background and elucidation of the scope and nature of the present invention, U.S. Pat. No. 563,836 is incorporated hereinto by reference. It is to be understood that literally thousands of issued United States patents and literally millions of light transmissive objects manufactured by mankind have existed and exist, many of these objects having prisms of varying character incorporated thereinto, Franck, in U.S. Pat. Nos. 2,818,500 and 2,887,568 discloses prisms generally useful in luminaire structures. Franck describes a variety of prisms, flutes and light-directing structures typically formed of glass and intended to efficiently illuminate areas in the vicinity of such luminaires. In U.S. Pat. No. 2,887,568, splitting prisms are mentioned as being useful for light direction in the illumination of an elongated environmental space such as a hallway. In U.S. Pat. No. 2,818,500, Franck describes the shaping of portions of prisms at apices and at valleys between adjacent prisms for reduction of light loss. Barnes et al, in U.S. Pat. Nos. 4,839,781 and 5,444,606, generally describe the use of prisms in globes used in luminaires and particularly in globes formed of “plastic” materials such as acrylic materials, these materials having come in more recent times to be used along with “glass” materials of varying description for the formation of globes used in luminaires. In U.S. Pat. No. 4,839,781, Barnes et al disclose a luminaire globe having differing kinds of prisms formed in differing zones to reflect and/or refract light for selective variation of light distribution depending on location of a light source within the luminaire. Barnes et al particularly describe vertical prisms of refractive or reflective characteristics, or both, as being useful in luminaire structures such as are disclosed with the choice of such prisms being dependent upon the location of a light source within a luminaire so configured.
Osteen, in U.S. Pat. Nos. 4,118,763 and 5,036,445, respectively describes globe members used within a luminaire and disposed about a light source, such globe members being constructed of light transmissive material having a variety of prismatic surfaces formed thereon which act in combination and in confluence with the shape of the globe member to produce light output in desirable directions. In U.S. Pat. No. 5,036,445, Osteen discloses a reflector structure having prisms capable of total internal reflection so that light exiting from the top of a globe member can be limited. Pearce, in U.S. Pat. No. 5,416,684, discloses the use of prisms formed on differing portions of a globe member for accomplishing desired light direction such as for increasing downward output of light from a luminaire. In U.S. Pat. No. 3,329,812, Harling discloses a particular refractor structure useful in a luminaire for light control through direction of light emanating from a light source to illuminate locations externally of the luminaire. Fouke, in U.S. Pat. No. 6,027,231, inter alia, describes globe members particularly useful in luminaires and formed of glass, acrylic materials and the like, for direction of light from a luminaire for efficient illumination. Kelly et al, in U.S. Pat. No. 5,434,765, describe a globe member having reflector and refractor sections and having prisms formed on surfaces of said sections for direction of light in a downward manner.
The United States patents mentioned above are only representative of a very substantial body of art that encompasses light transmissive reflector/refractor structures used in luminaires or the like wherein light output from a luminaire is controlled for direction into desired locations in the vicinity of such luminaires. Globe members used in such luminaires are light-transmissive members exhibiting either refractive, reflective or a combination of refractive and reflective properties, these properties occurring by virtue of the nature of prismatic and similar structures incorporated into such globe members. In this general area of lighting technology, light from a luminaire may be intended to directed upwardly, downwardly or both from a luminaire with the preponderance of light emanating from such a luminaire being intended as “uplight” or as “downlight”. Judicious selection of prismatic structures incorporated into such luminaire globe members permits light control and direction of light in a desired manner as has long been understood in the art.
Need often arises in the illumination arts for directing light into space located about a luminaire at an acceptable viewing angle with a minimum of glare. Various products manufactured and marketed by Acuity Brands, Inc. of Atlanta, Ga., formerly Holophane Corporation, under the trademark PRISMGLO utilize a particular kind of prism known as a splitter prism or splitting prism such as is shown in FIG. 5 of U.S. Pat. No. 563,836 to Blondel et al as referred to above. In the PRISMGLO luminaires, splitter prisms are used in order to take advantage of both total internal reflection and refraction to control light direction. Splitter prisms such as are used on PRISMGLO luminaires utilize linear or “straight line” sides or “flat” prismatic surfaces. Luminaire globe members of certain configurations with which splitter prisms can advantageously be employed have been found to be subject to light losses when splitter prisms having linear or straight sides or flat surfaces are utilized. Accordingly, the present invention intends the configuration of a splitter prism in particular that accomplishes light redirection more efficiently than is possible with splitter prisms configured according to the prior art. Prior art splitter prisms disposed on luminaire globe, members of certain shapes and with light incident thereon at certain angles of incidence unavoidably function to direct light onto an immediately adjacent prism. Light rays incident on the immediately adjacent prisms in such situations are redirected into the interior of the luminaire globe member or in some other direction such that the light is lost and the efficiency of the luminaire is thereby reduced. Splitter prisms configured according to the present invention and particularly functioning within particular environments as disclosed herein are formed so that light incident thereon is redirected in a manner so as to avoid incidence on immediately adjacent prisms, thereby allowing more light to enter a space being illuminated and thereby causing the luminaire to be more efficient. It is to be understood that the concept embodied by the several embodiments of the present invention can be applied to prisms of differing kind and not only to prisms such as could be referred to as “splitter prisms” or the like.